如何在Go或python中将struct写入文件？

Question

In C/C++, we can write a struct to file like this:

#include <stdio.h>
struct mystruct
{
    int i;
    char cha;
};

int main(void)
{
    FILE *stream;
    struct mystruct s;
    stream = fopen("TEST.$$$", "wb"))
    s.i = 0;
    s.cha = 'A';
    fwrite(&s, sizeof(s), 1, stream); 
    fclose(stream); 
    return 0;
}

But how to wirte a struct to file in go or python ? I want the data in struct are continuous.

Answer 1

In Python you can use ctypes module which allows you to generate structures with similar layout as C does, and convert them to byte arrays:

import ctypes

class MyStruct(ctypes.Structure):
    _fields_ = [('i', ctypes.c_int),
                ('cha', ctypes.c_char)]

s = MyStruct()
s.i = 0
s.cha = 'A'

f.write(bytearray(s))

There is a simplest approach in Python with using struct.pack and manually provide a layout as first argument ('ic' means int followed by a char):

import struct 
f.write(struct.pack('ic', 0, 'A'))

Go can encode structs via encoding/binary

type myStruct struct {
    i int 
    cha byte
}

s := myStruct{i: 0, cha:'A'}
binary.Write(f, binary.LittleEndian, &s)

NOTE: You will be subject of differing structure alignment, padding and endianness, so if you want to build truly interoperable program, use special formats such as Google Protobuf